Newhall states that dates given are earliest reference he located but unfortunately does not give the references. I don't think he had access to original pattern books, and most of his dates are from CGR.
From a source I am still preparing for publication in The Glass Study, Filip designs appear in CGR 1956/11, /12, 1958/13, 1960/15, 1961/2, /1,6 1962/16, 1962/17....etc. So one of those may give an answer.